This invention relates to a continuous process for electrostatically coating glass bottles, and other axially symmetrical objects with pulverized material, and an apparatus used in said process. More particularly, this invention relates to a continuous process for electrostatically coating an axially symmetrical object with pulverized synthetic resin and an apparatus used in said process, said process being characterized by electrostatically coating pulverized synthetic resin on the surface of an axially symmetrical object maintained at a temperature below the melting point of the pulverized synthetic resin, removing surplus pulverized synthetic resin (hereinafter referred to as "surplus powder") from the desired parts and then heating the pulverized resin-coated object so as to set and form a resin film on the surface of the axially symmetrical object.
Recently, it is desired to coat a film of synthetic resin on glass bottles of carbonated drinks such as Coca-Cola and the like in order to preventing the glass bottles from breaking during handling and/or because of a rise in internal pressure in the bottles due to sunlight. According to the conventional electrostatic coating process, it is usually necessary to preheat a glass bottle to a temperature above the melting point of the pulverized synthetic resin since a glass bottle is an electric insulator. That is, the conventional electrostatic coating process comprises preheating a glass bottle to a temperature above the melting point of the resin in order to lower the electrical resistance of glass, electrostatically coating pulverized synthetic resin on the preheated glass surface and then post-heating the resin-coated glass bottle to form a film of the resin on the surface of the glass bottle. However, according to this conventional process, it is almost impossible to remove the surplus pulverized resin adhering to the undesired part since the glass bottle is preheated. In order to prevent the pulverized resin from adhering to the undesired part (for example the mouth of the glass bottle), it is suggested to carry out the electrostatic coating while applying a gaseous jet stream to the vicinity of the mouth of the bottle to mask the mouth. However, even by this method, it is substantially impossible to completely mask the mouth of the bottle, and consequently the pulverized resin often adheres to the mouth part of the bottle covered by the cap, thus producing various serious problems such as incomplete capping or decapping and the incorporation of the resin film waste into the contents of the bottle. Moreover, the pulverized resin also adheres to the holding arm or chuck of the holding device, and due to the accumulated and fired resin, the operation of the apparatus must sometimes be suspended. In addition to the above mentioned disadvantages, the thickness of the resin film formed on the upper part of the bottle tends to be uneven and thin, thus resulting in the breakage or exfoliation of the resin film during washing or transportation of the resin-coated bottles. This is a serious problem for returnable glass bottles since the life of the glass bottle is shortened. Furthermore, for the purpose of improving the commercial value of glass bottles, the even coating of the resin film with uniform thickness is required. However, the conventional process comprising electrostatically coating the preheated glass bottle produces the above mentioned disadvantages and does not satisfy this requirement.